Various methods are known for the production of alkyl esters of aliphatic carboxylic acids, e.g., methyl methacrylate (MMA). One commercial method relies solely on acetone cyanohydrin (ACH) technology, i.e., the reaction of acetone with hydrogen cyanide to form ACH followed by acid-assisted hydrolysis and esterification with methanol to produce approximately 400 kilo-tons annually of MMA. Although the ACH route has traditionally been a core technology used in the United States and other parts of the world, lower cost alternative technologies are under consideration for future capacity increases. Several of these alternative technologies are ethylene-based. One such method is the hydroformylation of ethylene-to-propionaldehyde, followed by condensation to form methacrolein (MA) and subsequent oxidation and esterification to form MMA. Another route is the Alpha process that is commercially practiced by Lucite (currently owned by Mitsubishi Rayon). This is a two-step, liquid phase process that uses a homogeneous palladium-based catalyst to make methyl propionate which is then condensed with formaldehyde in a second step to make MMA. The process is described in WO 1999/021820. Other reports of homogenous catalysts for the liquid phase carbonylation of ethylene to methyl propionate include U.S. Pat. No. 3,507,891 (cobalt-pyridine catalyst), Chem. Commun., 2001, 47-48 (rhodium/b-ketophosphine catalyst); and J. Molecular Catalysis 40 (1987) 243-254, Hidai et al. (ruthenium-iodide catalyst).
One report of a heterogeneous catalyst that operates in the gas phase is by Bhattacharyya, S. K. and Nag, S. N., Brennstoff-Chemie, Vol. 43, p. 114-118 (1962). This work describes the use of metal iodides supported on silica gel for the synthesis of methyl propionate from ethylene, CO, and methanol in the gas phase. This process produces a large amount of undesirable by-product oxygenates and hydrocarbon compounds, and operates at a pressure of 253 bar (25.3 MPa).